Techniques for molding synthetic eye lenses from reactive materials have been shown in the art. For example, U.S. Pat. Nos. 4,209,289 and 4,402,659 disclose the use of mold halves which contact each other on blunt, flat surfaces that surround the periphery of the mold cavity. This technique has not proven to be entirely satisfactory. For example, the contacting flat surfaces must be as perfectly flat as possible so as to insure proper contact and alignment of the mold halves during the molding operation. This has proven to be very difficult to achieve as very slight variations in the flatness of these surfaces prevent the mold halves from being properly aligned.
U.S. Pat. Nos. 4,208,364 and 4,121,896 disclose the use of a mold having male and female mold sections. One of the sections employs a thin rim which contacts the molding surface of the other section. The rim flexes so that the two mold sections can approach each other and compensate for shrinkage of the lens material that occurs during polymerization.
This type of mold also has not proven entirely satisfactory. For example, the rim must be very thin in order to flex enough to compensate for the polymerization shrinkage. As a result, the rim is fragile and readily susceptible to damage. Consequently, extreme care must be taken in handling and storing the mold half with the rim on it.